Septic arthritis is an infection of the joint space by invading micro-organisms, commonly bacterial, which can cause considerable joint destruction.
Although this damage may be irreversible if treatment is delayed, early diagnosis and aggressive treatment can produce good results, making septic arthritis one of the few forms of arthritis where a total cure can be expected.
Because successful treatment hinges on early recognition, an emergency referral is indicated if a diagnosis of septic arthritis is suspected.
CAUSES OF INFECTION
In most cases, the joint becomes infected by a micro-organism carried through the blood from a distant site of infection. Sometimes direct spread from a nearby infected site or penetration of the joint area through injury is responsible for the infection.
A variety of micro-organisms can lead to septic arthritis. In children and young adults Staphylococcus aureus is common, while Neisseria gonorrhoeae is a possible pathogen.
Streptococci, viruses and other gram-negative pathogens can cause septic arthritis.
Septic arthritis can develop in children with no obvious risk factors, although usually sickle cell disease and immuno- suppression are predisposing factors. In adults, advancing age, an artificial joint already in place and malignancy are predisposing factors.
SYMPTOMS AND SIGNS
Typically, septic arthritis patients develop joint pain leading over a short period of time to a warm, erythematous joint with a significantly reduced range of movement.
Systemic symptoms such as general ill health or fever are possible, but are not always present. A hot, swollen joint is a typical presentation but some patients will present with multiple joint problems.
Older patients and those whose immune systems are compromised may present with non-specific ill health.
Children often present with typical symptoms, but in babies it can present by keeping the affected limb still or distress on moving it.
Generally speaking, septic arthritis usually affects a single large peripheral joint. In children the knee, hip and ankle are common sites of infection. In adults the knee, hip and shoulder are common sites.
A diagnosis of septic arthritis should be considered in all patients presenting with a hot swollen joint, however, there are other conditions with a similar presentation that should also be considered (see box).
Suspected septic arthritis patients should be seen urgently in secondary care for joint aspiration and synovial fluid analysis, including gram stain and culture. In addition, blood cultures should be taken. Other tests include FBC, measure of inflammatory markers, renal function and LFTs.
Plain X-rays may help to rule out other pathologies. Ultrasound can be used to guide aspiration or to confirm the presence of fluid.
MRI and CT scans can help in imaging joints that are difficult to assess.
The main thrust of treatment for septic arthritis is surgical drainage of the infected joint and antibiotic treatment to control the infection and reduce the severity of any possible joint damage.
In most cases, formal surgical or arthroscopic drainage of the affected joint is needed to remove necrotic material and intra-articular pus. This may need to be repeated more than once.
If closed joint procedures are not successful then more extensive joint surgery may be needed to drain the joint.
Intravenous antibiotics are started after culture material is obtained. A combination of clinical assessment and synovial fluid gram stain results are used to guide the initial choice of antibiotics. The final antibiotic regimen is decided by results of the synovial fluid culture.
After a few days of parenteral antibiotics, a switch can be made to oral antibiotics.
In some patients, three to four weeks of treatment are sufficient, depending on the infecting organism and the clinical state of the patient and their co-morbidities.
CONDITIONS SIMILAR TO SEPTIC ARTHRITIS
- Crystal arthritis/gout.
- Acute flare-up of inflammatory arthritis.
- Reactive arthritis: Reiter's syndrome, psoriatic arthritis, ankylosing spondylitis.
- Lyme disease.
- Viral arthritis: rubella, hepatitis B, HIV infection.